Induced Labor After C-Section Has Risks: Study

By Merritt McKinney

Wednesday July 4 5:55 PM ET

NEW YORK (Reuters Health) - After having a cesarean section, women who have induced labor for a subsequent birth are more likely to experience a potentially dangerous complication called uterine rupture--the reopening of the scar in their uterus-compared with women who have a repeat C-section, results of a new study show.

The risk of uterine rupture was particularly high among women whose labor was induced by hormones called prostaglandins, researchers at the University of Washington in Seattle report.

The findings come on the heels of a report in the May issue of the American Journal of Obstetrics and Gynecology (news - web sites) that found that women who have had C-sections are more likely to end up having a repeat C-section if labor is induced with drugs.

Every year about 60% of women who have had a C-section and become pregnant again attempt to have a vaginal delivery instead of another cesarean. This so-called ``trial of labor'' may be spontaneous or may be induced with drugs. But there have been concerns that a trial of labor in women who have already had a C-section may increase the risk of complications for the mother and child.

In the study, Dr. Mona Lydon-Rochelle and colleagues reviewed the records of more than 20,000 women in Washington State who had a C-section between 1987 and 1996, then had another child during that period.

Women who had a second C-section had the lowest rate of uterine rupture, the researchers report in the July 5th issue of The New England Journal of Medicine (news - web sites). For every 1,000 women who had a C-section, fewer than two experienced uterine rupture.

The rate was about three times greater (5.2 per 1,000 women) among women who had spontaneous labor and about five times greater (7.7 per 1,000 women) among women who had their labor induced with drugs other than prostaglandins.

The highest rate of uterine rupture--24.5 per 1,000 women--occurred in women who had their labor induced with prostaglandins. Their risk of uterine rupture was more than 15 times higher than it was for women who did not go through labor.

The American College of Obstetricians and Gynecologists advises against using one type of synthetic prostaglandin, misoprostol, to induce labor in women who have had surgery on their uterus.

Although Lydon-Rochelle and her colleagues were not able to determine which type of prostaglandin women in their study were given, they express doubt that the increased risk of uterine rupture was limited to misoprostol. The authors point out that misoprostol did not become widely used until 1996, the last year of the study, so other prostaglandins most likely increased the risk of uterine rupture as well.

``Whenever a woman has a cesarean section, the scar that is left in her uterus is never as strong as the original uterine tissue was before it was cut,'' Dr. Michael F. Greene of the Massachusetts General Hospital in Boston said in an interview.

``It was recognized more than 50 years ago that women who had prior cesarean sections have a significant risk that the old scar could reopen in that trial of labor,'' he told Reuters Health. But in the 1980s, medical practice began to change, with more women undergoing trial of labor after a C-section, he explained.

This study, which was considerably larger than most studies of uterine rupture, helps outline the true risks of trial of labor after C-section, he said.

Greene notes in an editorial that accompanies the study that doctors should discuss the risks with each woman who has had a C-section so she can make up her own mind about whether to attempt a trial of labor.

``Most reasonable women considering a trial of labor after a prior cesarean delivery would want to know that spontaneous labor is associated with a tripling of the risk of uterine rupture and that induction of labor with prostaglandins is associated with an increase in that risk by a factor of 15,'' he writes.

But to the question of what is safest for the baby, Greene says that the ``unequivocal answer'' is a repeat C-section.

SOURCE: The New England Journal of Medicine 2001;345:3-8, 54-55.

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